Routers form a central part of a data communication network and perform general routing. There can be multiple routers in a network. Information typically travels from one router to the next router, and eventually reaches the destination edge of the network. A destination edge router receives the information and decides where it goes from there. Typically it goes to an Internet service provider at the opposite edge of the edge router. If the destination is a household PC, the Internet service provider then sends the information to the destination computer. If there is corporate access to the network, the information may go from the edge router directly to a corporate site.
A fabric is a collection of devices which cooperatively provides a general routing capability. Internet protocol (IP) routers require protection from fabric failures, for example optical fabric, packet fabric, and switch element fabric failures. The prior art uses duplicated switch fabrics and line cards that feed both switch fabrics simultaneously but receive from only one switch fabric at any given time.
Internet protocol (IP) routers are not protected from line card failures with hot standby immediate acting protection mechanisms. Current designs depend on the external rerouting of IP packets and flows to restore packet traffic around failed line cards. This mode of protection is slow and is cumbersome to engineer and administer. A particular problem is that, in the event of failures of line cards or packet forwarding elements, it is impossible to limit the effects of those failures to the router in which the failure occurs. The downstream and upstream peer routers have to change their routing tables and change their packet destinations and flows in order to reroute packets around the failed packet forwarding line card.
An alternative approach is to implement multiple packet forwarding line cards to provide redundancy. This approach, however is economically unattractive, in that it consumes multiple switch fabric ports, thus doubling the required port count of the switch fabric. This results inevitably in underutilizing any particular line card. In order for additional packet traffic to be rerouted onto a line card M in the event of failure of line card N, a network must be engineered such that line card M is operating continuously at less than its maximum capacity.
Without fast acting hot standby protection, a network must be engineered with duplex and multiple routers and with less than fully utilized traffic capacity on each port. Then in the event of a facility or port failure during operation, all traffic must be redirected from the failed port to another port, which is available but underutilized and which has enough intrinsic capacity to carry the additional traffic under such a failure circumstance.
The first problem is not what happens once the failure occurs, but the way the network must be engineered to provide this complex protection structure. Once duplex routers or multiple routers are engineered into the network to address this type of failure, then typically it is required to engineer additional line capacity into the network between those routers. Whereas an unprotected network might require only a single trunk that is 100% utilized between two routers, a protected network under current technology requires a second trunk. The utilization of each one of the trunks in the absence of failure falls to only 50%. This increases the cost not only of the equipment, but of the router itself that now includes redundancy, software costs relating to the intervening network capacity, fiber optic transmission capacity including increased overhead traffic between routers, and administrative and engineering effort.
In prior art schemes an internal failure within a router would have to be protected by rerouting of the trunk outside of that router, perhaps encompassing several other routers in an existing network. Failure of a cable at a router can in fact propagate significantly far through a network, resulting in substantial confusion to the network as it adjusts to reconfigured routing. The network must broadcast to much of the Internet any IP addresses, for example, that have changed. Thus, small localized failures produce impacts that ripple out through the network, even though their original cause may not have been significant.
Not only do the packets get re-routed, but there is of necessity broadcast information that has to be sent to various routers to handle the re-routed traffic. In situations where outages occur from time to time, this can become overwhelming to a network. Even in the best case, the time to perform a repair and restore the original configuration can cause network traffic to slow dramatically. Again, this affects the capacity of a network, which in the initial stage would have to be engineered for higher capacity than would otherwise be necessary.
A common problem is an intermittent fault in a network, coming into and going out of service repetitively, thereby causing the generation of rerouting messages almost continuously through the network, known in the industry as “route-flap,” resulting in much non-useful traffic.
Consequently, there is a need in the optical network art for router systems and methods that provide protection in the event of a failure, requiring a smaller investment in equipment and engineering effort than in the prior art. Further, there is a need for router failure protection that requires minimal disruption and reconfiguration of the larger network, and that provides seamless continuity of service in the event of a single point of failure.